Originally Posted by user_none
Drivers in Calibre aren't the typical driver you're thinking of, like a driver for a graphics card. A driver in Calibre does not interface with the OS's kernel. All device drivers Calibre uses will work on any supported OS 32 or 64 bit. They are really just a way to tell Calibre how to write the files to the device. The Cybook and Kindle Drivers for instance were developed on a 64 bit Linux install.
That's true of all the drivers except the PRS 500 driver. The PRS 500 isn't a mass storage device, so calibre does need to interface with the USB subsystem to communicate with the device.